diff --git a/packages/react-art/src/ReactARTHostConfig.js b/packages/react-art/src/ReactARTHostConfig.js
index 47bced8a1274a..dbaba801b185a 100644
--- a/packages/react-art/src/ReactARTHostConfig.js
+++ b/packages/react-art/src/ReactARTHostConfig.js
@@ -451,3 +451,7 @@ export function preparePortalMount(portalInstance: any): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  // noop
+}
diff --git a/packages/react-dom/src/client/ReactDOMHostConfig.js b/packages/react-dom/src/client/ReactDOMHostConfig.js
index 4510efe2b892c..c9c6e11fdfe00 100644
--- a/packages/react-dom/src/client/ReactDOMHostConfig.js
+++ b/packages/react-dom/src/client/ReactDOMHostConfig.js
@@ -377,7 +377,10 @@ export const cancelTimeout: any =
   typeof clearTimeout === 'function' ? clearTimeout : (undefined: any);
 export const noTimeout = -1;
 const localPromise = typeof Promise === 'function' ? Promise : undefined;
-
+const localRequestAnimationFrame =
+  typeof requestAnimationFrame === 'function'
+    ? requestAnimationFrame
+    : scheduleTimeout;
 // -------------------
 //     Microtasks
 // -------------------
@@ -1379,3 +1382,9 @@ export function setupIntersectionObserver(
     },
   };
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  localRequestAnimationFrame(() => {
+    localRequestAnimationFrame(time => callback(time));
+  });
+}
diff --git a/packages/react-native-renderer/src/ReactFabricHostConfig.js b/packages/react-native-renderer/src/ReactFabricHostConfig.js
index 3ae1d00e27177..3c66e0ad8cd0b 100644
--- a/packages/react-native-renderer/src/ReactFabricHostConfig.js
+++ b/packages/react-native-renderer/src/ReactFabricHostConfig.js
@@ -611,3 +611,7 @@ export function preparePortalMount(portalInstance: Instance): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  // noop
+}
diff --git a/packages/react-native-renderer/src/ReactNativeHostConfig.js b/packages/react-native-renderer/src/ReactNativeHostConfig.js
index 37e88d8b2747b..c26c5c389c1e9 100644
--- a/packages/react-native-renderer/src/ReactNativeHostConfig.js
+++ b/packages/react-native-renderer/src/ReactNativeHostConfig.js
@@ -510,3 +510,7 @@ export function preparePortalMount(portalInstance: Instance): void {
 export function detachDeletedInstance(node: Instance): void {
   // noop
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  // noop
+}
diff --git a/packages/react-noop-renderer/src/createReactNoop.js b/packages/react-noop-renderer/src/createReactNoop.js
index f2b6fc8b255e9..66919fc89239d 100644
--- a/packages/react-noop-renderer/src/createReactNoop.js
+++ b/packages/react-noop-renderer/src/createReactNoop.js
@@ -473,6 +473,11 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
     logRecoverableError() {
       // no-op
     },
+
+    requestPostPaintCallback(callback) {
+      const endTime = Scheduler.unstable_now();
+      callback(endTime);
+    },
   };
 
   const hostConfig = useMutation
diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.new.js b/packages/react-reconciler/src/ReactFiberWorkLoop.new.js
index 6f62aa4b1c0b1..ca6bbcae278ab 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.new.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.new.js
@@ -261,6 +261,7 @@ import {
   suspendedThenableDidResolve,
   isTrackingSuspendedThenable,
 } from './ReactFiberWakeable.new';
+import {schedulePostPaintCallback} from './ReactPostPaintCallback';
 
 const ceil = Math.ceil;
 
@@ -361,6 +362,7 @@ export function getWorkInProgressTransitions() {
 }
 
 let currentPendingTransitionCallbacks: PendingTransitionCallbacks | null = null;
+let currentEndTime: number | null = null;
 
 export function addTransitionStartCallbackToPendingTransition(
   transition: Transition,
@@ -2643,6 +2645,36 @@ function commitRootImpl(
     markCommitStopped();
   }
 
+  if (enableTransitionTracing) {
+    // We process transitions during passive effects. However, passive effects can be
+    // processed synchronously during the commit phase as well as asynchronously after
+    // paint. At the end of the commit phase, we schedule a callback that will be called
+    // after the next paint. If the transitions have already been processed (passive
+    // effect phase happened synchronously), we will schedule a callback to process
+    // the transitions. However, if we don't have any pending transition callbacks, this
+    // means that the transitions have yet to be processed (passive effects processed after paint)
+    // so we will store the end time of paint so that we can process the transitions
+    // and then call the callback via the correct end time.
+    const prevRootTransitionCallbacks = root.transitionCallbacks;
+    if (prevRootTransitionCallbacks !== null) {
+      schedulePostPaintCallback(endTime => {
+        const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
+        if (prevPendingTransitionCallbacks !== null) {
+          currentPendingTransitionCallbacks = null;
+          scheduleCallback(IdleSchedulerPriority, () => {
+            processTransitionCallbacks(
+              prevPendingTransitionCallbacks,
+              endTime,
+              prevRootTransitionCallbacks,
+            );
+          });
+        } else {
+          currentEndTime = endTime;
+        }
+      });
+    }
+  }
+
   return null;
 }
 
@@ -2784,28 +2816,21 @@ function flushPassiveEffectsImpl() {
   if (enableTransitionTracing) {
     const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
     const prevRootTransitionCallbacks = root.transitionCallbacks;
+    const prevEndTime = currentEndTime;
     if (
       prevPendingTransitionCallbacks !== null &&
-      prevRootTransitionCallbacks !== null
+      prevRootTransitionCallbacks !== null &&
+      prevEndTime !== null
     ) {
-      // TODO(luna) Refactor this code into the Host Config
-      // TODO(luna) The end time here is not necessarily accurate
-      // because passive effects could be called before paint
-      // (synchronously) or after paint (normally). We need
-      // to come up with a way to get the correct end time for both cases.
-      // One solution is in the host config, if the passive effects
-      // have not yet been run, make a call to flush the passive effects
-      // right after paint.
-      const endTime = now();
       currentPendingTransitionCallbacks = null;
-
-      scheduleCallback(IdleSchedulerPriority, () =>
+      currentEndTime = null;
+      scheduleCallback(IdleSchedulerPriority, () => {
         processTransitionCallbacks(
           prevPendingTransitionCallbacks,
-          endTime,
+          prevEndTime,
           prevRootTransitionCallbacks,
-        ),
-      );
+        );
+      });
     }
   }
 
diff --git a/packages/react-reconciler/src/ReactFiberWorkLoop.old.js b/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
index 414e2e3343ed0..4715d3fdf4df9 100644
--- a/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
+++ b/packages/react-reconciler/src/ReactFiberWorkLoop.old.js
@@ -261,6 +261,7 @@ import {
   suspendedThenableDidResolve,
   isTrackingSuspendedThenable,
 } from './ReactFiberWakeable.old';
+import {schedulePostPaintCallback} from './ReactPostPaintCallback';
 
 const ceil = Math.ceil;
 
@@ -361,6 +362,7 @@ export function getWorkInProgressTransitions() {
 }
 
 let currentPendingTransitionCallbacks: PendingTransitionCallbacks | null = null;
+let currentEndTime: number | null = null;
 
 export function addTransitionStartCallbackToPendingTransition(
   transition: Transition,
@@ -2643,6 +2645,36 @@ function commitRootImpl(
     markCommitStopped();
   }
 
+  if (enableTransitionTracing) {
+    // We process transitions during passive effects. However, passive effects can be
+    // processed synchronously during the commit phase as well as asynchronously after
+    // paint. At the end of the commit phase, we schedule a callback that will be called
+    // after the next paint. If the transitions have already been processed (passive
+    // effect phase happened synchronously), we will schedule a callback to process
+    // the transitions. However, if we don't have any pending transition callbacks, this
+    // means that the transitions have yet to be processed (passive effects processed after paint)
+    // so we will store the end time of paint so that we can process the transitions
+    // and then call the callback via the correct end time.
+    const prevRootTransitionCallbacks = root.transitionCallbacks;
+    if (prevRootTransitionCallbacks !== null) {
+      schedulePostPaintCallback(endTime => {
+        const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
+        if (prevPendingTransitionCallbacks !== null) {
+          currentPendingTransitionCallbacks = null;
+          scheduleCallback(IdleSchedulerPriority, () => {
+            processTransitionCallbacks(
+              prevPendingTransitionCallbacks,
+              endTime,
+              prevRootTransitionCallbacks,
+            );
+          });
+        } else {
+          currentEndTime = endTime;
+        }
+      });
+    }
+  }
+
   return null;
 }
 
@@ -2784,28 +2816,21 @@ function flushPassiveEffectsImpl() {
   if (enableTransitionTracing) {
     const prevPendingTransitionCallbacks = currentPendingTransitionCallbacks;
     const prevRootTransitionCallbacks = root.transitionCallbacks;
+    const prevEndTime = currentEndTime;
     if (
       prevPendingTransitionCallbacks !== null &&
-      prevRootTransitionCallbacks !== null
+      prevRootTransitionCallbacks !== null &&
+      prevEndTime !== null
     ) {
-      // TODO(luna) Refactor this code into the Host Config
-      // TODO(luna) The end time here is not necessarily accurate
-      // because passive effects could be called before paint
-      // (synchronously) or after paint (normally). We need
-      // to come up with a way to get the correct end time for both cases.
-      // One solution is in the host config, if the passive effects
-      // have not yet been run, make a call to flush the passive effects
-      // right after paint.
-      const endTime = now();
       currentPendingTransitionCallbacks = null;
-
-      scheduleCallback(IdleSchedulerPriority, () =>
+      currentEndTime = null;
+      scheduleCallback(IdleSchedulerPriority, () => {
         processTransitionCallbacks(
           prevPendingTransitionCallbacks,
-          endTime,
+          prevEndTime,
           prevRootTransitionCallbacks,
-        ),
-      );
+        );
+      });
     }
   }
 
diff --git a/packages/react-reconciler/src/ReactPostPaintCallback.js b/packages/react-reconciler/src/ReactPostPaintCallback.js
new file mode 100644
index 0000000000000..a52623caa089b
--- /dev/null
+++ b/packages/react-reconciler/src/ReactPostPaintCallback.js
@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+import {requestPostPaintCallback} from './ReactFiberHostConfig';
+
+let postPaintCallbackScheduled = false;
+let callbacks = [];
+
+export function schedulePostPaintCallback(callback: (endTime: number) => void) {
+  callbacks.push(callback);
+  if (!postPaintCallbackScheduled) {
+    postPaintCallbackScheduled = true;
+    requestPostPaintCallback(endTime => {
+      for (let i = 0; i < callbacks.length; i++) {
+        callbacks[i](endTime);
+      }
+      postPaintCallbackScheduled = false;
+      callbacks = [];
+    });
+  }
+}
diff --git a/packages/react-reconciler/src/__tests__/ReactFiberHostContext-test.internal.js b/packages/react-reconciler/src/__tests__/ReactFiberHostContext-test.internal.js
index 82e23de9965da..19ddc6c8262f4 100644
--- a/packages/react-reconciler/src/__tests__/ReactFiberHostContext-test.internal.js
+++ b/packages/react-reconciler/src/__tests__/ReactFiberHostContext-test.internal.js
@@ -67,6 +67,7 @@ describe('ReactFiberHostContext', () => {
         return DefaultEventPriority;
       },
       supportsMutation: true,
+      requestPostPaintCallback: function() {},
     });
 
     const container = Renderer.createContainer(
@@ -129,6 +130,7 @@ describe('ReactFiberHostContext', () => {
       getCurrentEventPriority: function() {
         return DefaultEventPriority;
       },
+      requestPostPaintCallback: function() {},
       supportsMutation: true,
     });
 
diff --git a/packages/react-reconciler/src/__tests__/ReactTransitionTracing-test.js b/packages/react-reconciler/src/__tests__/ReactTransitionTracing-test.js
index a6637b55977c9..45dba5cd3c8a2 100644
--- a/packages/react-reconciler/src/__tests__/ReactTransitionTracing-test.js
+++ b/packages/react-reconciler/src/__tests__/ReactTransitionTracing-test.js
@@ -2273,4 +2273,231 @@ describe('ReactInteractionTracing', () => {
     });
     expect(Scheduler).toHaveYielded(['Hidden Text']);
   });
+
+  // @gate enableTransitionTracing
+  it('discrete events', async () => {
+    const transitionCallbacks = {
+      onTransitionStart: (name, startTime) => {
+        Scheduler.unstable_yieldValue(
+          `onTransitionStart(${name}, ${startTime})`,
+        );
+      },
+      onTransitionProgress: (name, startTime, endTime, pending) => {
+        const suspenseNames = pending.map(p => p.name || '<null>').join(', ');
+        Scheduler.unstable_yieldValue(
+          `onTransitionProgress(${name}, ${startTime}, ${endTime}, [${suspenseNames}])`,
+        );
+      },
+      onTransitionComplete: (name, startTime, endTime) => {
+        Scheduler.unstable_yieldValue(
+          `onTransitionComplete(${name}, ${startTime}, ${endTime})`,
+        );
+      },
+    };
+
+    function App() {
+      return (
+        <Suspense
+          fallback={<Text text="Loading..." />}
+          unstable_name="suspense page">
+          <AsyncText text="Page Two" />
+        </Suspense>
+      );
+    }
+
+    const root = ReactNoop.createRoot({
+      unstable_transitionCallbacks: transitionCallbacks,
+    });
+
+    await act(async () => {
+      ReactNoop.discreteUpdates(() =>
+        startTransition(() => root.render(<App />), {name: 'page transition'}),
+      );
+      ReactNoop.expire(1000);
+      await advanceTimers(1000);
+    });
+
+    expect(Scheduler).toHaveYielded([
+      'Suspend [Page Two]',
+      'Loading...',
+      'onTransitionStart(page transition, 0)',
+      'onTransitionProgress(page transition, 0, 1000, [suspense page])',
+    ]);
+    await act(async () => {
+      ReactNoop.discreteUpdates(() => resolveText('Page Two'));
+      ReactNoop.expire(1000);
+      await advanceTimers(1000);
+    });
+
+    expect(Scheduler).toHaveYielded([
+      'Page Two',
+      'onTransitionProgress(page transition, 0, 2000, [])',
+      'onTransitionComplete(page transition, 0, 2000)',
+    ]);
+  });
+
+  // @gate enableTransitionTracing
+  it('multiple commits happen before a paint', async () => {
+    const transitionCallbacks = {
+      onTransitionStart: (name, startTime) => {
+        Scheduler.unstable_yieldValue(
+          `onTransitionStart(${name}, ${startTime})`,
+        );
+      },
+      onTransitionProgress: (name, startTime, endTime, pending) => {
+        const suspenseNames = pending.map(p => p.name || '<null>').join(', ');
+        Scheduler.unstable_yieldValue(
+          `onTransitionProgress(${name}, ${startTime}, ${endTime}, [${suspenseNames}])`,
+        );
+      },
+      onTransitionComplete: (name, startTime, endTime) => {
+        Scheduler.unstable_yieldValue(
+          `onTransitionComplete(${name}, ${startTime}, ${endTime})`,
+        );
+      },
+    };
+
+    function App() {
+      const [, setRerender] = useState(false);
+      React.useLayoutEffect(() => {
+        resolveText('Text');
+        setRerender(true);
+      });
+      return (
+        <>
+          <Suspense unstable_name="one" fallback={<Text text="Loading..." />}>
+            <AsyncText text="Text" />
+          </Suspense>
+          <Suspense
+            unstable_name="two"
+            fallback={<Text text="Loading Two..." />}>
+            <AsyncText text="Text Two" />
+          </Suspense>
+        </>
+      );
+    }
+
+    const root = ReactNoop.createRoot({
+      unstable_transitionCallbacks: transitionCallbacks,
+    });
+
+    await act(() => {
+      startTransition(() => root.render(<App />), {name: 'transition'});
+      ReactNoop.expire(1000);
+      advanceTimers(1000);
+    });
+
+    expect(Scheduler).toHaveYielded([
+      'Suspend [Text]',
+      'Loading...',
+      'Suspend [Text Two]',
+      'Loading Two...',
+      'Text',
+      'Suspend [Text Two]',
+      'Loading Two...',
+      'onTransitionStart(transition, 0)',
+      'onTransitionProgress(transition, 0, 1000, [two])',
+    ]);
+
+    await act(() => {
+      resolveText('Text Two');
+      ReactNoop.expire(1000);
+      advanceTimers(1000);
+    });
+    expect(Scheduler).toHaveYielded([
+      'Text Two',
+      'onTransitionProgress(transition, 0, 2000, [])',
+      'onTransitionComplete(transition, 0, 2000)',
+    ]);
+  });
+
+  // @gate enableTransitionTracing
+  it('transition callbacks work for multiple roots', async () => {
+    const getTransitionCallbacks = transitionName => {
+      return {
+        onTransitionStart: (name, startTime) => {
+          Scheduler.unstable_yieldValue(
+            `onTransitionStart(${name}, ${startTime}) /${transitionName}/`,
+          );
+        },
+        onTransitionProgress: (name, startTime, endTime, pending) => {
+          const suspenseNames = pending.map(p => p.name || '<null>').join(', ');
+          Scheduler.unstable_yieldValue(
+            `onTransitionProgress(${name}, ${startTime}, ${endTime}, [${suspenseNames}]) /${transitionName}/`,
+          );
+        },
+        onTransitionComplete: (name, startTime, endTime) => {
+          Scheduler.unstable_yieldValue(
+            `onTransitionComplete(${name}, ${startTime}, ${endTime}) /${transitionName}/`,
+          );
+        },
+      };
+    };
+
+    function App({name}) {
+      return (
+        <>
+          <Suspense
+            unstable_name={name}
+            fallback={<Text text={`Loading ${name}...`} />}>
+            <AsyncText text={`Text ${name}`} />
+          </Suspense>
+        </>
+      );
+    }
+
+    const rootOne = ReactNoop.createRoot({
+      unstable_transitionCallbacks: getTransitionCallbacks('root one'),
+    });
+
+    const rootTwo = ReactNoop.createRoot({
+      unstable_transitionCallbacks: getTransitionCallbacks('root two'),
+    });
+
+    await act(() => {
+      startTransition(() => rootOne.render(<App name="one" />), {
+        name: 'transition one',
+      });
+      startTransition(() => rootTwo.render(<App name="two" />), {
+        name: 'transition two',
+      });
+      ReactNoop.expire(1000);
+      advanceTimers(1000);
+    });
+
+    expect(Scheduler).toHaveYielded([
+      'Suspend [Text one]',
+      'Loading one...',
+      'Suspend [Text two]',
+      'Loading two...',
+      'onTransitionStart(transition one, 0) /root one/',
+      'onTransitionProgress(transition one, 0, 1000, [one]) /root one/',
+      'onTransitionStart(transition two, 0) /root two/',
+      'onTransitionProgress(transition two, 0, 1000, [two]) /root two/',
+    ]);
+
+    await act(() => {
+      caches[0].resolve('Text one');
+      ReactNoop.expire(1000);
+      advanceTimers(1000);
+    });
+
+    expect(Scheduler).toHaveYielded([
+      'Text one',
+      'onTransitionProgress(transition one, 0, 2000, []) /root one/',
+      'onTransitionComplete(transition one, 0, 2000) /root one/',
+    ]);
+
+    await act(() => {
+      resolveText('Text two');
+      ReactNoop.expire(1000);
+      advanceTimers(1000);
+    });
+
+    expect(Scheduler).toHaveYielded([
+      'Text two',
+      'onTransitionProgress(transition two, 0, 3000, []) /root two/',
+      'onTransitionComplete(transition two, 0, 3000) /root two/',
+    ]);
+  });
 });
diff --git a/packages/react-reconciler/src/forks/ReactFiberHostConfig.custom.js b/packages/react-reconciler/src/forks/ReactFiberHostConfig.custom.js
index 9bb5d6e271c49..517b45ead8fc1 100644
--- a/packages/react-reconciler/src/forks/ReactFiberHostConfig.custom.js
+++ b/packages/react-reconciler/src/forks/ReactFiberHostConfig.custom.js
@@ -67,6 +67,7 @@ export const prepareScopeUpdate = $$$hostConfig.prepareScopeUpdate;
 export const getInstanceFromScope = $$$hostConfig.getInstanceFromScope;
 export const getCurrentEventPriority = $$$hostConfig.getCurrentEventPriority;
 export const detachDeletedInstance = $$$hostConfig.detachDeletedInstance;
+export const requestPostPaintCallback = $$$hostConfig.requestPostPaintCallback;
 
 // -------------------
 //      Microtasks
diff --git a/packages/react-test-renderer/src/ReactTestHostConfig.js b/packages/react-test-renderer/src/ReactTestHostConfig.js
index b452893ab2a9e..dfccf3e9ef0fc 100644
--- a/packages/react-test-renderer/src/ReactTestHostConfig.js
+++ b/packages/react-test-renderer/src/ReactTestHostConfig.js
@@ -317,3 +317,7 @@ export function detachDeletedInstance(node: Instance): void {
 export function logRecoverableError(error: mixed): void {
   // noop
 }
+
+export function requestPostPaintCallback(callback: (time: number) => void) {
+  // noop
+}